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>3TB HDD with SATA and/or USB3.0
HDDs are so cheap these days. You can get 4-6TB drives from Western Digital and Seagate for under $150. Affordable and high-volume. Sounds appealing. You could set up a RAID quite affordably, but that's not going to be very portable.
This is my go-to storage solution. They come with a limited 1 year hardware replacement warranty. But you have to foot the bill for data recovery, which isn't guaranteed to work. They're frequently problematic and unreliable. They typically fail completely within a few years. This seems to be intentional - i.e. designed to fail.
They used to be much more reliable ten years ago, but then again they were only about 256-500GB back then. Back then, they used to be regular, internal-style SATA HDDs with a Mini-USB adapter on a separate PCB, all bundled into a fancy enclosure. This made them very easy to troubleshoot, and you could get a generic adapter online for about $10. Now they're all on a single board with a proprietary adapter, and if you manage to separate them, surprise; the whole drive is encrypted at that level now anyway, because that's totally necessary for the average consumer.
2.5" Solid State Drives
Prices for these are all over the place, but they're not cheap. @ ~6Gb/s: 4TB Samsung for ~$1,000. 2 TB Crucial for ~$500. 1TB WD Blue, SanDisk, Samsung Portable for ~$300. They're quick, they live a long time, I don't know the warranties because they're kind of expensive, so I don't buy a lot of them. But they're pretty great.
>100GB SD & Micro-SD Cards
I like SanDisk Ultra, Extreme, and Extreme Pro; 128-256GB Micro SD cards with the regular SD adapter that most modern Digital SLR and Mirrorless cameras use. You can usually get them for under $200
They're fast, reliable, have no moving parts, come with a 10 year warranty, and you can probably count on them lasting significantly longer than your lifetime if you look after them and store them well. Personally, I love Pelican cases for hardware storage and transport. And I like their CF & SD card storage cases. Other brands with similar products include Neewer, Honsky, Kupton, etc. Check Amazon.
If it were more cost effective, I would just use these. All day, every day. One card per project. Labels. Colour coded. Pelican cases. Wall safe. Problem solved. But it quickly adds up. So I use these for their speed, transfer images, and re-use them over and over again.
Storage solutions by Google, Dropbox, Adobe, and probably a hundred others; are super convenient and super reliable. They seem inexpensive, but it adds up eventually, and that cost is recurring. And I don't know what happens to your data when you can't afford to keep making those payments. Sounds dicey.
So, what's a reliable, cost-effective solution to the modern photographers data storage problem?